Polyhalogenated organic substances such as polychlorinated biphenyls (PCB) have been used in many systems either as hydraulic fluid, heat exchange media or dielectric components in electrical transformers or condensers. In spite of excellent technical performances however, the environmental problems associated with the use of such substances has led to their withdrawal from previously widespread applications.
The substitution of non halogenated hydrocarbons to PCB has led in many cases to mixtures of various composition of non halogenated and halogenated materials. Since some environmental protection agencies have ruled that concentrations as low as one part per million of PCB in mineral oils used in electrical equipments or as hydraulic fluids was objectionable, even a slight contamination of a given lot of non halogenated mineral oil by some residual PCB left in a piece of equipment generates an environmental pollution in the case of a spill or leak.
It is to be underlined here that non halogenated oils used in electrical equipments or hydraulic systems is relatively expensive, the cost being of the order of several dollars per liters. Therefore, a slight contamination by PCB, by rendering a given charge of mineral oil improper for use corresponds to a serious monetary loss if the whole contaminated lot has to be discarded or destroyed for the sake of a few ppm of PCB.
Therefore it has been found desirable to use a method by which a given lot of mineral oil contaminated by polyhalogenated organic material could be freed of said polyhalogenated contaminants while the mineral oil thus cleaned would be recovered for further use, without degradation.
It is well known to organic chemists that halogenated organic molecules can be reacted with sodium, with the corresponding formation of sodium halide. This type of reaction designated by the name of their conceptors:Wurtz or Wurtz-Fittig were already known at the turn of this century (Organic Chemistry, Fieser & Fieser, 3rd edition (1956) pp. 35 and 534). For the destruction of a substance such as hexachlorobenzene, the equation of the process is: EQU C.sub.6 Cl.sub.6 +6Na.fwdarw.6NaCl+6C
Using such a reaction, PCB or other halogenated materials can be destroyed while non halogenated mineral oils contaminated by a minor amount of halogenated material are not affected by the action of sodium.
The implementation of such a treatment by metallic sodium has been recommended in several recent patents for the purification of mineral oils contaminated by PCB. For example, Norman (U.S. Pat. No. 4,379,752), Norman and Handler (U.S. Pat. No. 4,379,746) and Jordan (U.S. Pat. No. 4,340,471) have recommended the use of fine dispersions of metallic sodium in hydrocarbons as an efficient method of removal of minor amounts of PCB from said hydrocarbons. The recommended operational temperatures are spread over a range of 75.degree. C. to 150.degree. C. Other patents indicate the use of sodium combined with aromatic anions (Parker and Sabo, U.S. Pat. No. 4,447,667) or with alcohols of various structures: Pytlewski, Iaconianni et al, U.S. Pat. No. 4,417,977 and Pytlewski and Thorne, U.S. Pat. No. 4,430,208. These reagents incorporating the sodium are used after their formation for the treatment of the contaminated oils.
The implementation of these recommended protocols has been found in practice as not too practical or attractive. The fine dispersions of sodium particles, in the micron range size, are very reactive initially but when the reaction has started with the PCB, the sodium soon gets coated with the sodium halide resulting from the reaction; it agglomerates in lumps and loses much of its reactivity. For those reasons, substantial excess of sodium are required to achieve the treatment and residues after treatment still containing sizable amounts of unreacted metal, such pyrophoric material creating handling problems. Also, because of the coating of the sodium, rather long reaction times are required, generally measured in hours. This may lead to some degradation of the oil exposed to such a long period at temperature often above 125.degree. C. When sodium is combined with aromatic anion or alcohols, the recovery of these substrates for sodium render the operation of treatment both complex and economically non attractive.
Therefore it is obvious that a process simple in its operation and allowing for a fast reaction would be highly desirable.